Fix update of volatile rates

app/strconv/currates/__init__.py

@@ -40,13 +40,16 @@ def update_rates(src: Iterable[DataSource]) -> None:
     :raises ExternalServiceError: if something bad happened while executing request
     """
 
+    src = list(src)
+
     global __src_cache
     if len(__src_cache) == 0:
         _logger.info("Filling the cache of currency rates sources...")
-        __src_cache = src = list(src)
+        __src_cache = src
 
     today = datetime.datetime.utcnow().date()
-    if 'date' in __db and __db['date'].decode() == str(today):
+    volatile = all(x.volatile for x in src)
+    if not volatile and 'date' in __db and __db['date'].decode() == str(today):
         _logger.info("The cache already has the actual currency exchange rates. Skipping...")
         return